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                Design Pattern - Builder Pattern
              
            
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        <span itemprop="articleBody"><p>Builder pattern builds a complex object using simple objects and using a step by step approach. This type of design pattern comes under creational pattern as this pattern provides one of the best ways to create an object.</p>
<p>A Builder class builds the final object step by step. This builder is independent of other objects.</p>
<h4 id="Implementation">Implementation</h4><p>We have considered a business case of fast-food restaurant where a typical meal could be a burger and a cold drink. Burger could be either a Veg Burger or Chicken Burger and will be packed by a wrapper. Cold drink could be either a coke o pepsi and will be packed in bottle.</p>
<p>We are going to create an Item interface representing food items such as burgers and cold drinks and concrete classes implementing the Item interface and a Packing interface representing packaging of food items and concrete classes implementing the Packing interface as burger would be packed in wrapper and cold drink would be packed as bottle.</p>
<p>We then create a Meal class having ArrayList of item and a MealBuilder to build different types of Meal objects by combining item. BuilderPatterDemo, our demo class will use MealBuilder to build a Meal.</p>
<p><img src="images/builder_pattern_uml_diagram.jpg" alt="builder_pattern_uml_diagram"></p>
<a id="more"></a>
<h4 id="Step_1">Step 1</h4><p>Create an interface item representing food item and packing.</p>
<p><strong>Item.java</strong><br><figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">public</span> <span class="class"><span class="keyword">interface</span> <span class="title">Item</span></span>&#123;</span><br><span class="line">    <span class="function"><span class="keyword">public</span> String <span class="title">name</span><span class="params">()</span></span>;</span><br><span class="line">    <span class="function"><span class="keyword">public</span> Packing <span class="title">packing</span><span class="params">()</span></span>;</span><br><span class="line">    <span class="function"><span class="keyword">public</span> <span class="keyword">float</span> <span class="title">price</span><span class="params">()</span></span>;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure></p>
<p><strong> Packing.java</strong><br><figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">public</span> <span class="class"><span class="keyword">interface</span> <span class="title">Packing</span></span>&#123;</span><br><span class="line">    <span class="function"><span class="keyword">public</span> String <span class="title">pack</span><span class="params">()</span></span>;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure></p>
<h4 id="Step_2">Step 2</h4><p>Create concrete classes implementing the Packing interfac.</p>
<p><strong>Wrapper.java</strong></p>
<figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">public</span> <span class="class"><span class="keyword">class</span> <span class="title">Wrapper</span> <span class="keyword">implements</span> <span class="title">Packing</span></span>&#123;</span><br><span class="line"></span><br><span class="line">    <span class="annotation">@Override</span></span><br><span class="line">    <span class="function"><span class="keyword">public</span> String <span class="title">pack</span><span class="params">()</span></span>&#123;</span><br><span class="line">        <span class="keyword">return</span> <span class="string">"Wrapper"</span>;</span><br><span class="line">    &#125;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>
<p><strong>Bottle.java</strong><br><figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">public</span> <span class="class"><span class="keyword">class</span> <span class="title">Bottle</span> <span class="keyword">implements</span> <span class="title">Packing</span></span>&#123;</span><br><span class="line">    <span class="annotation">@Override</span></span><br><span class="line">    <span class="function"><span class="keyword">public</span> String <span class="title">pack</span><span class="params">()</span></span>&#123;</span><br><span class="line">        <span class="keyword">return</span> <span class="string">"Bottle"</span>;</span><br><span class="line">    &#125;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure></p>
<h4 id="Step_3">Step 3</h4><p>Create abstract classes implementing the item interface providing default functionalities.</p>
<p><strong>Burger.java</strong><br><figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">public</span> <span class="keyword">abstract</span> <span class="class"><span class="keyword">class</span> <span class="title">Burger</span> <span class="keyword">implements</span> <span class="title">Item</span></span>&#123;</span><br><span class="line">    <span class="annotation">@Override</span></span><br><span class="line">    <span class="function"><span class="keyword">public</span> Packing <span class="title">packing</span><span class="params">()</span></span>&#123;</span><br><span class="line">        <span class="keyword">return</span> <span class="keyword">new</span> Wrapper();</span><br><span class="line">    &#125;</span><br><span class="line">   </span><br><span class="line">    <span class="annotation">@Override</span></span><br><span class="line">    <span class="function"><span class="keyword">public</span> <span class="keyword">abstract</span> <span class="keyword">float</span> <span class="title">price</span><span class="params">()</span></span>;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure></p>
<p><strong>ColdDrink.java</strong></p>
<figure class="highlight"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br></pre></td><td class="code"><pre><span class="line">public abstract class ColdDrink implements Item&#123;</span><br><span class="line"></span><br><span class="line">    @Override</span><br><span class="line">    public Packing packing()&#123;</span><br><span class="line">        return new Bottle();</span><br><span class="line">    &#125;</span><br><span class="line"></span><br><span class="line">    @Override</span><br><span class="line">    public abstract float price();</span><br><span class="line">&#125;</span><br><span class="line"></span><br><span class="line">#### Step 4</span><br><span class="line"></span><br><span class="line">Create concrete classes extending Burger and ColdDrink classes</span><br><span class="line"></span><br><span class="line">**VegBurger.java**</span><br><span class="line"></span><br><span class="line">```java</span><br><span class="line">public class VegBurger extends Burger&#123;</span><br><span class="line">   </span><br><span class="line">    @Override</span><br><span class="line">    public float price()&#123;</span><br><span class="line">        return 25.0f;</span><br><span class="line">    &#125;</span><br><span class="line"></span><br><span class="line">    @Override</span><br><span class="line">    public String name()&#123;</span><br><span class="line">        return "Veg Burger";</span><br><span class="line">    &#125;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>
<p><strong>ChickenBurger.java</strong></p>
<figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">public</span> <span class="class"><span class="keyword">class</span> <span class="title">ChickenBurger</span> <span class="keyword">extends</span> <span class="title">Burger</span></span>&#123;</span><br><span class="line"></span><br><span class="line">    <span class="annotation">@OVerride</span></span><br><span class="line">    <span class="function"><span class="keyword">public</span> <span class="keyword">float</span> <span class="title">price</span><span class="params">()</span></span>&#123;</span><br><span class="line">        <span class="keyword">return</span> <span class="number">50.5f</span>;</span><br><span class="line">    &#125;</span><br><span class="line"></span><br><span class="line">    <span class="annotation">@Override</span></span><br><span class="line">    <span class="function"><span class="keyword">public</span> String <span class="title">name</span><span class="params">()</span></span>&#123;</span><br><span class="line">        <span class="keyword">return</span> <span class="string">"Chicken Burger"</span>;</span><br><span class="line">    &#125;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>
<p><strong>Coke.java</strong><br><figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">public</span> <span class="class"><span class="keyword">class</span> <span class="title">Coke</span> <span class="keyword">extends</span> <span class="title">ColdDrink</span></span>&#123;</span><br><span class="line"></span><br><span class="line">    <span class="annotation">@Override</span></span><br><span class="line">    <span class="function"><span class="keyword">public</span> <span class="keyword">float</span> <span class="title">price</span><span class="params">()</span></span>&#123;</span><br><span class="line">        <span class="keyword">return</span> <span class="number">30.3f</span>;</span><br><span class="line">    &#125;</span><br><span class="line"></span><br><span class="line">    <span class="annotation">@Override</span></span><br><span class="line">    <span class="function"><span class="keyword">public</span> String <span class="title">name</span><span class="params">()</span></span>&#123;</span><br><span class="line">        <span class="keyword">return</span> <span class="string">"Coke"</span>;</span><br><span class="line">    &#125;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure></p>
<p><strong>Pepsi.java</strong><br><figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">public</span> <span class="class"><span class="keyword">class</span> <span class="title">Pepsi</span> <span class="keyword">extends</span> <span class="title">ColdDrink</span></span>&#123;</span><br><span class="line"></span><br><span class="line">    <span class="annotation">@Override</span></span><br><span class="line">    <span class="function"><span class="keyword">public</span> <span class="keyword">float</span> <span class="title">price</span><span class="params">()</span></span>&#123;</span><br><span class="line">        <span class="keyword">return</span> <span class="number">23.3f</span>;</span><br><span class="line">    &#125;</span><br><span class="line"></span><br><span class="line">    <span class="annotation">@Override</span></span><br><span class="line">    <span class="function"><span class="keyword">public</span> String <span class="title">name</span><span class="params">()</span></span>&#123;</span><br><span class="line">        <span class="keyword">return</span> <span class="string">"Pepsi"</span>;</span><br><span class="line">    &#125;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure></p>
<h4 id="Step_5">Step 5</h4><p>Create a Meal class having item objects defined above.</p>
<p><strong>Meal.java</strong><br><figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">import</span> java.util.ArrayList;</span><br><span class="line"><span class="keyword">import</span> java.util.List;</span><br><span class="line"></span><br><span class="line"><span class="keyword">public</span> <span class="class"><span class="keyword">class</span> <span class="title">Meal</span></span>&#123;</span><br><span class="line">    </span><br><span class="line">    <span class="keyword">private</span> List&lt;Item&gt; items = <span class="keyword">new</span> ArrayList&lt;Item&gt;();</span><br><span class="line"></span><br><span class="line">    <span class="function"><span class="keyword">public</span> <span class="keyword">void</span> <span class="title">addItem</span><span class="params">(Item item)</span></span>&#123;</span><br><span class="line">        items.add(item);</span><br><span class="line">    &#125;</span><br><span class="line"></span><br><span class="line">    <span class="function"><span class="keyword">public</span> <span class="keyword">float</span> <span class="title">getCost</span><span class="params">()</span></span>&#123;</span><br><span class="line">        <span class="keyword">float</span> cost = <span class="number">0.0f</span>;</span><br><span class="line"></span><br><span class="line">        <span class="keyword">for</span> (Item item : items)&#123;</span><br><span class="line">            cost += item.price();</span><br><span class="line">        &#125;</span><br><span class="line">        <span class="keyword">return</span> cost;</span><br><span class="line">    &#125;</span><br><span class="line"></span><br><span class="line">    <span class="function"><span class="keyword">public</span> <span class="keyword">void</span> <span class="title">showItems</span><span class="params">()</span></span>&#123;</span><br><span class="line"></span><br><span class="line">        <span class="keyword">for</span>(Item item : items)&#123;</span><br><span class="line">            System.out.print(<span class="string">"Item : "</span> + item.name());</span><br><span class="line">            System.out.print(<span class="string">", Packing : "</span> + item.packing().pack());</span><br><span class="line">            System.out.println(<span class="string">", Price : "</span> + item.price());</span><br><span class="line">        &#125;</span><br><span class="line">    &#125;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure></p>
<h4 id="Step_6">Step 6</h4><p>Create a MealBuilder class, the actual builder class responsible to create Meal objects.</p>
<p><strong>MealBuilder.java</strong></p>
<figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">public</span> <span class="class"><span class="keyword">class</span> <span class="title">MealBuilder</span></span>&#123;</span><br><span class="line">   </span><br><span class="line">    <span class="function"><span class="keyword">public</span> Meal <span class="title">prepareVegMeal</span><span class="params">()</span></span>&#123;</span><br><span class="line">        Meal meal = <span class="keyword">new</span> Meal();</span><br><span class="line">        meal.addItem(<span class="keyword">new</span> VegBurger());</span><br><span class="line">        meal.addItem(<span class="keyword">new</span> Coke());</span><br><span class="line">        <span class="keyword">return</span> meal;</span><br><span class="line">    &#125;</span><br><span class="line"></span><br><span class="line">    <span class="function"><span class="keyword">public</span> Meal <span class="title">prepareNonVegMeal</span><span class="params">()</span></span>&#123;</span><br><span class="line">        Meal meal = <span class="keyword">new</span> Meal();</span><br><span class="line">        meal.addItem(<span class="keyword">new</span> ChickenBurger());</span><br><span class="line">        meal.addItem(<span class="keyword">new</span> Pepsi());</span><br><span class="line">        <span class="keyword">return</span> meal;</span><br><span class="line">    &#125;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>
<h4 id="Step_6-1">Step 6</h4><p>BuilderPatternDemo uses MealBuilder to demonstrate builder pattern.</p>
<p><strong>BuilderPatternDemo.java</strong></p>
<p>```java<br>public class BuilderPatternDemo{</p>
<pre><code><span class="function"><span class="keyword">public</span> <span class="keyword">static</span> <span class="keyword">void</span> <span class="title">main</span>(<span class="params">String[] args</span>)</span>{

    MealBuilder builder = <span class="keyword">new</span> MealBuilder();

    Meal vegMeal = builder.prepareVegMeal();
    System.<span class="keyword">out</span>.println(<span class="string">"veg meal"</span>);
    vegMeal.showItems();
    System.<span class="keyword">out</span>.println(<span class="string">"Total cost: "</span> + vegMeal.getCost());

    Meal nonVegMeal = builder.prepareNonVegMeal();
    System.<span class="keyword">out</span>.println(<span class="string">"\n\nNon-Veg Meal"</span>);
    nonVegMeal.showItems();
    System.<span class="keyword">out</span>.println(<span class="string">"Total Cost: "</span> + nonVegMeal.getCost());
}
</code></pre><p>}</p>
<h4 id="Step_8">Step 8</h4><p>Verify the output.</p>
<p>`<br>Veg Meal<br>Item : Veg Burger, Packing : Wrapper, Price : 25.0<br>Item : Coke, Packing : Bottle, Price : 30.0<br>Total Cost: 55.0</p>
<p>Non-Veg Meal<br>Item : Chicken Burger, Packing : Wrapper, Price : 50.5<br>Item : Pepsi, Packing : Bottle, Price : 35.0<br>Total Cost: 85.5<br>`</p>
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